Conventional deck blocks are made of Portland cement and sand mix and weigh between 42 and 51 lbs., each depending on the dimensions of the manufacturing moulds. These blocks are sold on pallets and transported by flat bed transport trailers. These cement blocks are expensive to transport and difficult to manipulate by clients. Concrete deck blocks are displayed for sale outside, in the yard of a hardware store for example, and clients are expected to load the blocks themselves in their vehicles. Because conventional deck blocks are too heavy to be displayed inside a hardware store, these blocks are sold mostly to carpenters and landscape contractors, and remain generally unknown to the do-it-yourself market.
The load bearing capacity of these blocks is equivalent to the compressive strength of the cement mix, which varies between 3000-6000 psi, generally.
Conventional construction blocks are described in the following documents:    U.S. Pat. No. 2,522,149, issued to W. Tunstall on Sep. 12, 1950;    U.S. Pat. No. 3,706,168, issued to A. Pilish on Dec. 19, 1972;    U.S. Pat. No. 4,328,651, issued to M. Gutierrez on May 11, 1982;    U.S. Pat. No. 4,724,642, issued to P. Hoffman et al., on Feb. 16, 1988;    U.S. Pat. No. 5,163,967, issued to P. Hoffman et al., on Nov. 17, 1992;    U.S. Pat. No. 5,392,575, issued to P. Hoffman et al., on Feb. 28, 1995;    U.S. Pat. No. 5,560,171, issued to J. R. McCoy on Oct. 1, 1996;    U.S. Pat. No. 5,953,874, issued to P. Hoffman et al., on Sep. 21, 1999;    U.S. Pat. No. 6,324,801, issued to P. Hoffman et al., on Dec. 4, 2001;    U.S. Pat. No. 6,345,474, issued to D. Triplett on Feb. 12, 2002; U.S. Pat. No. 7,827,747, issued to G. R. George et al., on Nov. 9, 2010.
A lightweight cement block has been developed in a recent past. These lightweight blocks are manufactured and sold by Featherlight Precast Products, of 35 South Street, Hancock, Md., 21750, USA. These lightweight deck blocks weigh 16 lbs each, and are more appropriate for display inside a hardware store where they can be seen and purchased by homeowners and handymen. The load bearing capacity of these lightweight blocks is 1,760 pounds each.
Although the capacity of the lightweight block is not as much as the conventional Portland cement block, it is stronger than the load bearing capacity of most soils on which the block will be installed. Also, the selling of these lightweight blocks with spacing instructions makes more sense commercially, than selling a heavy conventional block that has a compressive strength which largely exceeds the requirement of the actual load to be supported.
In the light of the above, it also makes sense to consider the manufacturing of deck blocks using a material that is lighter than concrete, providing that the blocks have a load bearing capacity that is reasonable for the intended application. Therefore, it is believed that there is a market for a plastic deck block that can be displayed for sale inside a hardware store and easily carried to a vehicle and easily installed by a handy homeowner.